I have data among several variables sampled from deep-sea sites located in a marine canyon. In total 13 sites (n=3/site) were sampled. Sampling was conducted on 5 sites along 1 transect (~ 500 - 2200 m), 5 sites on another transect (~500 - 1800 m), and 3 sites on another transect (~ 770 - 1000 m). Each transect represents a different treatment. The sampling design is unbalanced and it has been suggested that incomplete block design could be used to test for differences among my treatments. Is this a valid suggestion? What would my blocking factor be? New to blocking designs so I would appreciate any insight. Thanks in advance.